Communications Network Overview
In a typical cellular system, also referred to as a wireless communications network, wireless terminals or wireless devices, also known as mobile stations and/or user equipments (UEs) communicate via a Radio Access Network (RAN) to one or more core networks. The wireless terminals can be mobile stations or user equipment units such as mobile telephones also known as “cellular” telephones, and laptops with wireless capability, e.g., mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-comprised, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a Radio Base Station (RBS), which in some networks is also called “NodeB” or “B node” and which in this document also is referred to as a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units within range of the base stations.
In some versions of the radio access network, several base stations are typically connected, e.g., by landlines or microwave, to a Radio Network Controller (RNC). The radio network controller, also sometimes termed a Base Station Controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies. Long Term Evaluation (LTE) together with Evolved Packet Core (EPC) is the newest addition to the 3GPP family.
During operations, a user equipment will obtain bandwidth information from system information broadcast by a cell. The bandwidth information is a key parameter used for many purposes. Bandwidth information and the process for obtaining such information are described in greater detail below.
Bandwidth Information
In a cellular network a user equipment performs intra-frequency, inter-frequency, and/or inter-RAT measurements. FIG. 1A illustrates example intra-frequency scenarios. In all these scenarios the center frequency of the “target cell” and of the “current cell” are the same. However their bandwidth may or may not be the same. Furthermore the “target cell” is a measured cell, and a “current cell” is a serving cell (multiple serving cells may be utilized with carrier aggregation, for example, one PCell and one or more SCells). FIG. 1B illustrates example inter-frequency scenarios, where a “target cell” is a measured cell, and a “current cell” is a serving cell (multiple serving cells may be utilized with carrier aggregation, e.g., one PCell and one or more SCells). The target cell may be of the same or different RAT, which would result in an inter-RAT measurement. The bandwidth may be UL or DL bandwidth, which may or may not be the same. However in all the inter-frequency scenarios the center frequency of the “target cell” and of the “current cell” is not the same, for example, their center frequencies are shifted in the frequency domain.
In LTE, different bandwidth definitions exist. One example bandwidth definition in LTE is channel bandwidth. Channel bandwidth is the RF bandwidth supporting a single E-UTRA RF carrier with the transmission bandwidth configured in the uplink or downlink of a cell. The channel bandwidth is measured in MHz and is used as a reference for transmitter and receiver RF requirements.
A further example is a transmission bandwidth which is the bandwidth of an instantaneous transmission from a user equipment or BS, measured in Resource Block units. Yet another example is a transmission bandwidth configuration which is the highest transmission bandwidth allowed for uplink or downlink in a given channel bandwidth, measured in Resource Block units.
Another example is an aggregated channel bandwidth which is the RF bandwidth in which a base station or user equipment transmits and receives multiple contiguously aggregated carriers. The aggregated channel bandwidth is measured in MHz. Yet a further example is a subblock bandwidth which is the bandwidth of one subblock, where the subblock is one contiguous allocated block of spectrum for transmission and reception by the same base station or user equipment. There may be multiple instances of subblocks within an RF bandwidth. A further example is a measurement bandwidth which is the bandwidth over which a measurement is performed. The measurement bandwidth of a signal cannot exceed its transmission bandwidth.
Examples of such bandwidths are provided in the figures. FIG. 2A illustrates a channel bandwidth and transmission bandwidth configuration for an E-UTRA carrier. FIG. 2B illustrates an aggregated channel bandwidth for an intra-band carrier aggregation. FIG. 2C illustrates a sub-block bandwidth for an intra-band non-contiguous spectrum.
The bandwidth information is one of the key parameters used for many purposes, for example, for adapting receiver configuration for performing a measurement. Normally, the bandwidth information is read from system information broadcasted by the cell, for example, from MIB transmitted via PBCH.
System Information
In LTE, the system information is divided into the MasterInformationBlock (MIB) and a number of SystemInformationBlocks (SIBs). MIB defines the most essential physical layer information of the cell required to receive further system information. MIB comprises parameters such as dl-Bandwidth, phich-Config, and systemFrameNumber.
The MIB is mapped on the BCCH and carried on BCH while all other SI messages are mapped on the BCCH and dynamically carried on DL-SCH where they may be identified through the SI-RNTI (System Information RNTI). MIB is transmitted according to a fixed schedule with a periodicity of 40 ms in subframes #0. To improve MIB detection performance, 3 redundancy versions are also signaled with 10 ms period.
SystemInformationBlockType1 comprises information relevant when evaluating if a user equipment is allowed to access a cell and defines the scheduling of other system information blocks, including SIB2. SIB1 may be broadcasted or transmitted in dedicated signaling in a RRCConnectionReconfiguration message at HO or for inter-cell interference purpose. UL bandwidth (if different from DL bandwidth) may be transmitted in SIB2.